1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to disk drives, head stack, head gimbal and suspension assemblies that include conductive features used for alignment and placement of load beam and/or flexure features.
2. Description of the Prior Art
A typical hard disk drive includes a head disk assembly (“HDA”) and a printed circuit board assembly (“PCBA”). The HDA includes at least one magnetic disk (“disk”), a spindle motor for rotating the disk, and a head stack assembly (“HSA”) that includes a slider with at least one transducer or read/write element for reading and writing data. The HSA is controllably positioned by a servo system in order to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator assembly that moves in response to the servo control system; (2) a head gimbal assembly (“HGA”) that extends from the actuator assembly and biases the slider toward the disk; and (3) a flex cable assembly that provides an electrical interconnect with minimal constraint on movement.
A typical HGA includes a load beam, a flexure (also called a gimbal) attached to an end of the load beam, and a slider attached to the flexure. The load beam has a spring function that provides a “gram load” biasing force and a hinge function that permits the slider to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator arm and a flexure end that connects to the flexure that supports the slider and transmits the gram load biasing force to the slider to “load” the slider against the disk. A rapidly spinning disk develops a laminar airflow above its surface that lifts the slider away from the disk in opposition to the gram load biasing force. The slider is said to be “flying” over the disk when in this state.
Early HGAs included a number of twisted wires within a tube attached to a side of the actuator arm to electrically couple the slider to the preamplifier. However, more recent developments in the disk drive industry, such as the continuing miniaturization of slider assemblies (including the head and the transducer) and the transition to magnetoresistive (MR) heads have led to abandoning such configurations in favor of a configuration in which conductive traces are laid on a polyimide film formed on or coupled to the gimbal assembly. Such technologies are variously named TSA (Trace Suspension Assembly), CIS (Circuit Integrated Suspension, FOS (Flex On Suspension) and the like. Whatever their differences, each of these technologies replaces the discrete twisted wires with conductive traces (copper, for example) and insulating (such as polyimide, for example) and support or cover layers (including stainless steel, for example). These conductive traces interconnect the transducer elements of the head to the drive preamplifier and the circuits associated therewith.
To enable the slider to fly over the recording surface of the disk, the load beam, near its distal-most free end, has a dimple formed therein. The spherical outline of the dimple enables the slider to exhibit some measure of pivot movement (e.g., pitch and roll) relative to the flexure. As track densities increase, slider dimensions may correspondingly decrease. As these dimensions decrease, the proper positioning of the dimple formed in the load beam becomes increasingly important. Conventionally, a variety of holes and cutouts in the load beam are used to provide a spatial reference for the formation of this dimple. Alternatively, holes and/or cutouts on the frame on which the suspension assemblies are formed may be used as spatial references or registration features for the proper alignment and positioning of the dimple. These holes and/or cutouts may be used by machine vision systems and/or pins inserted therethrough to align and position the dimple to be formed within the load beam. During the manufacture of the TSA, a masking and etching process is used to form the laminate flexure, which is then welded onto the load beam. The TSA includes a plurality of conductive traces as well as four or more bonding pads to electrically couple the slider to the preamplifier. The slider itself includes at least four bonding pads configured to align with the bonding pads on the TSA. As the size and pitch of the bonding pads is quite small (currently may be about 75 microns and about 113 microns, respectively), it is imperative that the bonding pads on the flexure be precisely located relative to the dimple to insure the flyability of the slider. Positioning of the slider relative to the dimple will affect flyability and the positioning of the flexure bonding pads will affect the yield of the slider to flexure bonding. However, because the dimple is formed relative to features (e.g., cutouts and other registration features) of the load beam and as the bonding pads on the flexure are formed by a separate masking and etching process that uses different spatial references, positioning errors stack up. That is, the tolerances for the formation of the bonding pads and for the formation of the dimple add to one another. As the dimensions of the slider and associated features decrease, these added tolerances become a non-negligible factor relative to the size of the slider and bonding pads and can affect the positioning of the flexure bonding pads and the slider relative to the dimple and by extension, the flyability of the slider over the recording surface of the disk.
An exemplary conventional TSA-type HGA 100 is shown in FIG. 1. FIG. 1 shows the surface of the HGA 100 that faces the recording surface of the disk when the HSA incorporating the HGA 100 is mounted within a disk drive. As shown therein, the conventional HGA includes a load beam 102 that may attach to an actuator arm (not shown in FIG. 1) of an HSA (also not shown in FIG. 1) through, for example, a swaging process through an opening 101 defined within the load beam 102. The TSA includes a flexure 104 that is coupled to the load beam 102. The flexure 104 includes a plurality of conductors that electrically couple a slider to the preamplifier of the HSA. As shown in FIG. 1, the flexure defines flexure bonding pads 113 to which corresponding bonding pads of the slider (not shown) electrically connect. The load beam 102 of conventional HGA 100 of FIG. 1 includes a plurality of load beam features, at reference numerals 108, 112 and 116. These features are shown in FIG. 1 as being cutouts defined within the load beam 102. The flexure 104 may also include one or more flexure registration features. For example, the flexure 104 may define a flexure registration feature 106 that is formed so as to align with the underlying load beam feature 108 and a flexure registration feature that is formed so as to align with the underlying load beam feature 112. The dimple 114 is also shown in FIG. 1, formed within the load beam 102, at the distal free end thereof. Conventionally, the dimple 114 is not formed at the same time (or using the same process) as the load beam features 108, 112 or the flexure registration feature(s). Indeed, while the load beam 102 is etched to form the load beam features 108, 112 and 114, a forming process is employed to form the dimple 114, by means of a local deformation of the load beam to form the spherical dimple 114. As the bonding pads 113, the flexure registration features 106, 110 and the dimple 114 do not use the same positional references, positioning errors stack up (add), which has the potential to cause the misalignment of the flexure bonding pads 113 relative to the dimple 114 and the misalignment of the flexure bonding pads 113 relative to the corresponding pads on the slider. It is to be noted that, when bonding the slider to the flexure 104, the flexure bonding pads 114 are not used as positional references.
From the foregoing, it may be appreciated that improved disk HSAs, HGAs, suspensions and disk drives are needed in which the dimple is precisely positioned relative to the flexure bonding pads and in which the above-detailed cumulative positional errors are eliminated or minimized.